Collaborative Research: Time-Dependent Hydrothermal Convection within the Great Basin, Nevada

合作研究：内华达州大盆地内随时间变化的热液对流地下水流是否仅限于由自由对流驱动的高渗透断层？或者，水流是由地下水位地形梯度和某种组合的基质和断层控制的流体循环驱动的吗？这些系统从根本上是暂时的和自封闭的，是由于高大的矿化作用，还是由于碳酸盐溶解而提高了渗透率？为了评估这些问题，我们将使用一种新的并行有限元程序(PGEOFE)开发一套适用于大盆地内两个现场的3D单相热液模型。我们将利用现代Beowawwe地热系统的一个新的三维(3-D)地质模型，并与美国地质调查局的同事一起开发另一个始新世Carlin系统的三维地质模型；这两个地点拥有丰富的同位素、地球化学和地热数据集。使用LaGRIT网格生成软件，这些水文地质模型将遵循已知的断层几何形状、宽度和地层学。该网格生成软件将允许我们在网格从地层过渡到断层时遵循低网格长宽比(Aztec并行求解器软件包所要求的)，同时允许在求解热和质量传输方程时进行足够的细化以最大限度地减少数值网格分散。我们将使用多种约束来约束我们的模型，这些约束包括温度分布、浅层热流图、流体/岩石成分以及温泉矿床的年龄。在Beowawe，通过测定烧结矿阶地中的花粉和附近裸露矿脉中的adualria，我们可以了解热流体沿着断层周期性排放的时间，以及烧结矿矿床记录的这种排放的持续时间。将使用PFLOTRAN开发更复杂的反应-运移地球化学模型，以评估每个系统中增加孔隙度的碳酸盐溶解反应和封闭的脉石沉淀反应。我们的模型将通过比较现代和化石的地球化学和热学指标来验证。该项目将支持新墨西哥理工大学和密苏里大学哥伦比亚分校的两名研究生。初步结果将提交给来自Beowawe发电厂、巴里克金矿和纽蒙特金矿的行业代表，供他们提供意见和反馈，以改进最终结果。结果将在2010年内华达州地质学会研讨会和科学期刊上发表，以接触到当地和国际观众。

Collaborative Research: Time-Dependent Hydrothermal Convection within the Great Basin, NevadaIs groundwater flow restricted to high permeability fault planes driven by free-convection? Or, is flow driven by water-table topographic gradients with some combination of matrix and fault controlled fluid circulation? Are these systems fundamentally transient and self-sealing due to gaunge mineralization, or , is permeability enhanced by carbonate dissolution? To evaluate these problems we will develop a suite of 3D, single-phase, hydrothermal models using a new parallel finite element code (PGEOFE) for two field sites within the Great Basin. We will utilize a new three-dimensional (3-D) geologic model of the modern Beowawe geothermal system and, with USGS colleagues, develop another 3-D geologic model of the Eocene Carlin system; two sites with rich , isotopic, geochemical and geothermal data sets. Using LaGrit mesh generation software, these hydrogeologic models will honor known fault geometries, widths, and stratigraphy. This mesh generation software will allow us to honor low grid aspect ratios (required by the AZTEC parallel solver package) as the grid transitions from strata to faults while allowing sufficient refinement to minimize numerical grid dispersion when solving the heat and mass transport equations. We will use multiple constraints including temperature profiles, shallow heat flow maps, fluid/rock ä 18O composition, and the age of hot springs deposits to constrain our models. At Beowawe, by dating pollen in the sinter terrace and adualria in exposed veins nearby we can get a sense of the timing of episodic discharges of hot fluid up the faults and on the duration of such discharges recorded by the sinter deposits. More sophisticated reactive-transport geochemical models will be developed using PFLOTRAN to evaluate porosity-enhancing carbonate dissolution reactions and ?sealing gangue precipitation reactions in each system. Our models will be validated by comparing modern and fossil geochemical and thermal proxies . The project will support two graduate students at New Mexico Tech and University of Missouri at Columbia. Initial results will be presented to industry representatives from Beowawe power plant, Barrick and Newmont gold mines for their input and feedback to improve the final result. Results will be published at the Geological Society of Nevada 2010 symposium and scientific journals to reach local and international audiences.